The reletion between nutrition and exhibition of the gene antennales ( Drosophila melanogaster )

Abstract

The gene Antennaless located on the second chromosome of Drosophila melanogaster prevents formation of antennae under appropriate conditions of culture. In normal cultures phenotypic indices (§1) of pure lines are at first high, then decline to a minimum about the fourth day, and subsequently rise to near the initial level. This emergence effect is not due to selective mortality of genotypes dis­tinguished by modifiers of Antennaless. It is due to external changes in normal culture media. As indicated by the temperature-effective period of the normal fully fed larva, the time of action of the gene is between the third and fourth days of larval life. Within a small range examined (5°C), temperature changes have a striking effect on exhibition, when the medium is sterile. On normal media, changing behaviour of yeast populations masks this effect. An apparent association between changing pH of a normal medium and changing frequency of exhibition in a normal culture is brought about by a complex series of interacting agencies. It is possible to correlate successive changes of exhibition frequency in a normal culture with: ( a ) gross changes due to the activities of the larvae; ( b ) biochemical changes in the yeast diet arising from differential fertility or mortality of yeast strains and from the direct action of changing conditions upon the metabolism of the microflora. Yeasts produce X substances which, encourage, and Y substances which inhibit, exhibition of the gene Antennaless. The relative proportions of X and Y substances vary in accordance with: ( a ) yeast strains used in the same environment; ( b ) different external conditions to which the same strain responds. A provisional hypothesis suggested by data derived both from study of gross changes in a normal culture and from analysis of yeast fractions is that: ( a ) transition from the descending to the ascending phase of exhibition coincides with change from aerobic to anaerobic respiration of the yeasts; ( b ) this change of yeast metabolism affects the relative concentrations of specific nutritional products which influence exhibition. Among yeast constituents normally required by Drosophila one fraction, which is adsorbed by charcoal, lowers the frequency of exhibition. Vitamin B 2 has a similar effect, and is partly responsible for the observed inhibitory effects of certain yeast fractions.